Matt_H has selflessly and patiently lent his time and knowledge in helping me plan and execute this initial portion of the build for a while now. I’d like to thank that man right off the bat.
Here we have, a serious(-ly awesome) mutt.
This is a prototype that will be completely re-built. Once we’ve figured out what’s desirable and necessary, versus what’s not so attractive or practical, gone through all the tweaks and twerks and abolished all living amp gremlins that may be… THEN, all updated materials will be used to re-embody this thing into a shiny new enclosure, SUPER clean style. That being said, this “chassis” has been repurposed from an old power amp prototype chassis. It’s ugly, it’s patchworked, but it damn sure does the job for now.
The Iron has been sourced from free, or otherwise on the cheap. The PT was what started this thing, and was acquired from an old Orion tube volt meter. Fo Free. The OT is from a Marshall DSL 50, a Dagnall TXOP 00002. I think I have about 20 bucks in it. The choke was about the same, and was kinda specific so I bought it new. Weighing in at 5 Henries, 400VDC, 150mA… the Hammond 158Q.
To get the current of the PT up to the task, a choke input filter was in order. This particular one has had mostly all of the current drawn across it in testing thus far, and it exhibits two warnings. 1) A VERY minor buzz that can be heard by having your ear almost pressed against it. 2) At power down, it emits a small “chirp”. I’ve got my eye on FeeBay for a 5-10H 200mA (or more) choke. …Unless you have one? Still, not too worried about it yet.
The OT is less than ideal here, we’re aware. (Estimations are of that it’s a 3K4 zpri) Mismatching speaker loads is gonna happen.
Ghetto UL. “Heretical”, yet has been established as a very praise-worthy design, with the help of Matt. It’s been executed by others, as can be seen in Dave Root’s thread “And Now For Something Completely Different”. This thread is actually what really got my attention as to the Ghetto UL concept in the first place. Awesome amp that gentleman has over there!
There’s a Full blown phase inverter in this little champion. No “faux PI” here! Half is for the output section, and the remaining half will be put to some use… A line level out, probably.
The preamp is a modded flavor of The Yeti, JCM 800, etc. chosen for its well documented and executable design. Also, it sounds good, and it’s generally tweak-friendly.
Lotsa other “different” stuff…
The cathode follower is bootstrapped, and has the accommodation (on the schematic) for the added protective neon bulb current limiter. That’ll be an add-in after it’s running, and depending on whether or not it induces noise, another route will be taken. (This is Merlin Blencowe stuff)
Rotary knob of clipping diodes, etc. This’ll mostly be borrowed/adapted from the findings of another great fellow TAG member, Reeltarded. (Squish knob will be in there too!) I looked at the usual suspects among diodes, LED’s, Transistors, and got everything in-between to give it all a go. This area on the schem is blank, for good reason. Gotta ear test a whole buncha stuff! (Hey Miles!)
Slope adjustment pot, labeled “Freq Tweak”. Yep, that’s neat.
------------------------------------------------------------------------------------
This amp has gotten as far as the power supply, the bias network being proven to work and in the range we’re looking for, and most of the other assembly done. Nothing has smoked, caught fire, or threatened to do so yet… So, it’s presented to you thus far in progress! (Not gonna lie, we were a little scared)
This is not at all your average amp, on many points, I think that’s the main reason I’m so attracted to it already.
(Be nice!
)So far we’re looking at about 385VDC B+ loaded. All other voltages are within spec/to be expected. We’ll get to that info when the time comes. (Soon-ish!)
As far as I know, the schem and layout are right up to what's in there, or, going to be in there. Aside from the bright switches in the schematic, they'll actually be done like in the layout instead. (I think?)
